A(1) Field of the invention
The invention generally relates to a stand-alone utility device for general consumer use and more particularly to those devices which only function properly if they are operated by authorized persons.
Stand-alone is herein understood to mean that the utility device can operate independently, like a car radio or another audio apparatus, a television receiver and the like. Such an apparatus is not subordinate to an external device and thus does not function like a peripheral apparatus which is subordinate to a central computer.
A(2) Description of the prior art
Modern stand-alone utility devices are generally provided with a plurality of independent or interrelated processing circuits which in very modern apparatuses are controlled by a control circuit in the form of a microcomputer. They receive status data from the microcomputer or apply status data to this computer. These status data indicate the state of a processing circuit, or the state to which it must be set. In a broadcasting receiver these status data represent, for example the frequency to which the receiver is tuned, the treble, volume, balance, etc.
To apply further status data to the different processing circuits, a plurality of keys are coupled to the microcomputer which comprises an internal non-volatile memory with a plurality of addressable memory locations each being addressable by means of a program counter. Each memory location comprises a processing step. A plurality of associated processing steps is referred to as control program. The number of such control programs stored in the internal non-volatile memory differs from device to device. A frequently occurring control program is the switch-on program performed in response to a switch-on command which is generated when switching on the device. Start-status data are then applied to the different processing circuits. For a broadcasting receiver this means that it is tuned to a given transmitter, while a given value is also assigned to the treble, balance, contrast, colour saturation, etc.
The sophisticated character of such stand-alone utility devices makes them a very attractive object for thieves. Particularly the number of car radio thefts has considerably increased in the last few years. To deter these thefts, the car radio was initially anchored mechanically in the car dashboard or console. However, this appeared to be insufficiently effective and moreover it resulted in the car interior being seriously damaged in the case of theft. Therefore it was later proposed to anchor the car radio in a position which was not visible or was hardly accessible, for example, under one of the car seats or in the trunk. To operate this car radio, a separate control panel was supplied which could be built in, for example in the steering wheel and was coupled to the car radio via a remote control system. Apart from the fact that these measures were still found to be inadequate in many cases, the use of a remote control system had a strong price-increasing effect.
The most modern way of rendering a car radio and generally a stand-alone utility device unattractive to thieves is the use of a so-called security program or "electronic lock". This is a control program in the microcomputer which is performed when a so-called security command is generated. This may be the case whenever the car radio is switched on if, after interruption the supply of power, supply voltage to the microcomputer is resumed. If this control program is executed, the receiver is said to be electronically locked and it does not function. The user is requested to identify himself by stating his so-called identity code. He can do this by using the control keys, or in a different way. The identity code stated by the user is compared with an antitheft code which is stored in the car radio in an antitheft code memory intended for this purpose. Only if the two codes are identical to each other is the receiver electronically unlocked, which means that it functions normally.
Initially, this had been arranged in such a way that the owner of the receiver itself could get access to the antitheft code memory in order to store or change an antitheft code which he had devised himself. Besides, the receiver was supplied without an antitheft code to the supplier. At that moment and during transport from the manufacturer to the customer, the receiver was not protected against theft. This was found to be a drawback in practice. However, the situation became even more serious when an ever increasing number of motorcar manufacturers started to build in car radios in their cars and subsequently transported this combination to the customer. Notably during this transport large quantities of car radios were stolen. For this reason the car radio manufacturer decided to store an antitheft code in the antitheft code memory, which antitheft code is different from car radio to car radio and is only made known to the customer. This has the drawback that such a car radio, after having been built in the car, cannot be checked by the car manufacturer on its correct operation, or if in fact the car radio has been built in properly.